Organic advantage? Take a closer look

May 15, 2008|By HAROLD McGEE The New York Times

"New evidence confirms the nutritional superiority of plant-based organic foods." So proclaims the title of a report published in March by the Organic Center, an advocacy organization supported by food and grocery companies. To my eyes, the evidence confirms how little good information we really have.

The Organic Center report collects meaningful nutritional comparisons of produce grown with and without the application of synthetic fertilizers, herbicides and pesticides. It's not easy to isolate the effects of any one factor in a process as complicated and unpredictable as agriculture.

The Organic Center devised a screening method to identify well-executed experiments, and identified a total of 236 valid comparisons of particular nutrients in particular fruits and vegetables. They found organic foods to be nutritionally superior in 61 percent of the comparisons, notably for vitamin C, vitamin E and anti-oxidant activity.

A data set of 236 comparisons sounds large and inspires confidence. But it covers 11 nutrients and more than a dozen crops. So it turns out that there are only two or three independent studies of, for example, vitamin C in tomatoes, or anti-oxidants in apples. That hardly seems to justify the report's ringingly conclusive "Yes, organic plant-based foods are, on average, more nutritious." Reliable information is still pretty sparse.

And conventional produce appears to contain consistently higher levels of protein and beta carotene. The Organic Center report explains this away with two analogies to human metabolism. It likens the heavy use of nitrogen fertilizer in conventional agriculture to a candy-induced "sugar high" and to taking steroids to build muscle mass. This suggests that nitrogen fertilizer is unnatural and unhealthy for the plant, its nutritional benefits somehow tainted.

I asked a plant scientist, Arthur R. Grossman of the Carnegie Institution for Science, whether heavy doses of fertilizer distort normal plant metabolism. Grossman tells me that plants have evolved to cope with the broad range of growing conditions, and they adjust their biochemical machinery as needed. Some levels of plant chemicals will go up and others will go down depending on the supply of light, water, nitrogen and other minerals.

It's likely that there will never be a clear winner in the conventional vs. organic battle if they are judged strictly by comparing their nutrient score cards. Grossman suggests that organic farming may have a more general nutritional advantage over a system that relies on agricultural chemicals.

"I think it's likely that plants grown with minimal intervention by the farmer are chemically more complex," he says. "If they experience some low level of stress from pests and fluctuating soil and light conditions, they'll use their biochemical machinery to make continual adjustments, and they may develop a more diverse set of chemical compounds.

"The biochemical machinery in plants is incredibly prolific," Grossman says. "They can make hundreds of relatives of beta carotene alone. I'm sure we haven't identified all the beneficial chemicals in plants. And diversity in the molecules we consume may be beneficial in itself."